Co-Authors:
Bourras, S., Institute of Plant Biology, University of Zurich, Zürich, Switzerland
McNally, K.E., Institute of Plant Biology, University of Zurich, Zürich, Switzerland
Ben-David, R., Institute of Plant Sciences, Agricultural Research Organization, Volcani Center, Bet Dagan, Israel, Institute of Plant Biology, University of Zurich, Zürich, Switzerland
Parlange, F., Institute of Plant Biology, University of Zurich, Zürich, Switzerland
Roffler, S., Institute of Plant Biology, University of Zurich, Zürich, Switzerland
Praz, C.R., Institute of Plant Biology, University of Zurich, Zürich, Switzerland
Oberhaensli, S., Institute of Plant Biology, University of Zurich, Zürich, Switzerland
Menardo, F., Institute of Plant Biology, University of Zurich, Zürich, Switzerland
Stirnweis, D., KWS Saat, Grimsehlstrasse 31, Einbeck, Germany, Institute of Plant Biology, University of Zurich, Zürich, Switzerland
Frenkel, Z., Institute of Evolution, University of Haifa, Mount Carmel, Haifa, Israel
Schaefer, L.K., Institute of Plant Biology, University of Zurich, Zürich, Switzerland
Flückiger, S., Institute of Plant Biology, University of Zurich, Zürich, Switzerland
Treier, G., Institute of Plant Biology, University of Zurich, Zürich, Switzerland
Herren, G., Institute of Plant Biology, University of Zurich, Zürich, Switzerland
Korol, A.B., Institute of Evolution, University of Haifa, Mount Carmel, Haifa, Israel
Wicker, T., Institute of Plant Biology, University of Zurich, Zürich, Switzerland
Keller, B., Institute of Plant Biology, University of Zurich, Zürich, Switzerland
Abstract:
In cereals, several mildew resistance genes occur as large allelic series; for example, in wheat (Triticum aestivum and Triticum turgidum), 17 functional Pm3 alleles confer agronomically important race-specific resistance to powdery mildew (Blumeria graminis). The molecular basis of race specificity has been characterized in wheat, but little is known about the corresponding avirulence genes in powdery mildew. Here, we dissected the genetics of avirulence for six Pm3 alleles and found that three major Avr loci affect avirulence, with a common locus_1 involved in all AvrPm3-Pm3 interactions. We cloned the effector gene AvrPm3a2/f2from locus_2, which is recognized by the Pm3a and Pm3f alleles. Induction of a Pm3 alleledependent hypersensitive response in transient assays in Nicotiana benthamiana and in wheat demonstrated specificity. Gene expression analysis of Bcg1 (encoded by locus_1) and AvrPm3a2/f2revealed significant differences between isolates, indicating that in addition to protein polymorphisms, expression levels play a role in avirulence. We propose a model for race specificity involving three components: an allele-specific avirulence effector, a resistance gene allele, and a pathogenencoded suppressor of avirulence. Thus, whereas a genetically simple allelic series controls specificity in the plant host, recognition on the pathogen side is more complex, allowing flexible evolutionary responses and adaptation to resistance genes. ©2015 American Society of Plant Biologists. All rights reserved.